As is well known, various tool holders have been utilized in the prior art which interface with a rotating spindle of a machine such as a milling or boring machine to securely hold a cutting tool upon the machine during the cutting of a work piece. In most prior art tool holders, a central aperture is formed therein for receiving the shank portion of the cutting tool which is to be interfaced to the milling or other machine. Subsequent to the insertion of the shank portion of the cutting tool into the central aperture, the tool holder is drawn or pulled tightly into the spindle so as to rigidly maintain the cutting tool within the tool holder.
Though interfacing the cutting tool to the machine, the prior art tool holders possess certain deficiencies which detract from their overall utility. In particular, when the elongate, extended shank of a long reach cutting tool is inserted into and secured within the central aperture of the tool holder, there is a tendency for a harmonic resonance to be generated through the cutting tool and into the tool holder, particularly when the cutting tool is used in a high speed milling application. The transfer of the harmonic resonance into the tool holder gives rise to slight movements thereof relative to the spindle, and in extreme cases results in the tool holder loosening within the spindle. As will be recognized, the resonance of the tool holder relative to the spindle results in the cut in the work piece being substantially out of tolerance.
A further deficiency with the prior art tool holders is that the manner in which the shank portion of the cutting tool is secured within the central aperture of the tool holder often results in the non-concentric mounting of the cutting tool within the tool holder. Such non-concentric mounting is unacceptable in modern, high tolerance machining applications such as those performed on a vertical milling machine wherein minor variations in the concentricity of the cutting tool within the tool holder often times causes catastrophic failure in the cutting operation.
The present invention addresses the deficiencies of prior art tool holders by providing a tool holder which includes a dampening member for eliminating the harmonic resonance which typically occurs when long reach, extended shank cutting tools are used in high speed milling applications. In the tool holder constructed in accordance with the present invention, the non-concentric mounting of the shank portion of the cutting tool within the tool holder is also substantially eliminated by the heat shrinking the shank portion of the cutting tool within the tool holder.